Process for finishing and testing lenses



F. TWYMAN.

PROCESS FOR FINISHING AND TESTING LENSES.

APPLICATION FILED FEB- 4.1919.

Patented Aug. 9, 1921.,

4 SHEETS-SHEET l- F. TWYMAN. PROCESS FOR FINISHING AND TESTING LENSES.

APPLICATION FILED FEB-4,19I9- Patented Aug. 9, 1921.

4 SHEETS-SHEET 2.

F. TWYMAN.

PROCESS FOR FINISHING AND TESTING LENSES.

APPLICATION FILED FEB. 4. I919.

1,886,663 Patented Aug. 9, 1921.

4 SHEETSPSHEET 3.

I F. TWYMAN.

PROCESS IfOR FINISHING AND TESTING LENSES. APPLICATION FILED FEB-4,1919.

1,3 6, 63., Patented Aug. 9,1921.

4 SHEETS -SHEET 4.

UNHTED stares PATIENT @FFHCE,

FRANK TWYMAN, OF LONDON, ENGLAND, ASSIGNOR TO ADAM HILGER, LIMITED, OF

LONDON, ENGLAND.

PROCESS; FOR FINISHING AND TESTING LENSES.

menses.

Specification of Letters Patent.

Patented Aug. 9,1921.

To all whom it may concern.

Be it known that I, FRANK TWYMAN, a subject of the King of Great Britain, resid ing at 75 Camden road, London, England, have invented a new and useful Improved Process for Finishing and Testing Lenses, of which the following is a specification.

This invention relates to improvements in the process for-finishing and testing lenses described in the specification of Patent No. 1,252,512 of Jan. 8, 19l8,.and is especially applicable for finishing lenses for use 1n cameras.

According to this invention, the lens is tested and corrected not only for beams of light entering the lens in an axial direction, but also for beams entering in oblique directions. The lens may be first tested and corrected for axial beams as described in the above mentioned patent, and subsequently tested and corrected for oblique beams. Or, since the correction for axial beams has efl'ect on the oblique beams and vice versa, it is in practice simpler to make partial corrections .for axial and oblique beams alternately until the greatest possible perfection is attained. V

In order to test'the lens for oblique beams it is turned about an axis at right angles to its optical axis and passing through the second principal or nodal point, and the beams passing through thelens are reflected back in a similar manner to that described in the former specification.

In an apparatus for carrying out this be noted. The mirror (which may be either concave or convex) by which the light is reflected back through thelens is adjustably mounted on a carriage, and the carriage is automaticallymoved toward or away from the lens so that 'the center of curvature of the mirror is always in the focal plane in which the lens is supposed to form its image. In order to accomplish this a flexible connection is led from: the carriage to a weight, and upon the carriage is a lug which is retained continually in contact with the bar above mentioned by the action of the weight.

The annexed drawings show an apparatus for carrying out this invention. Figure 1 is a plan, Fig. 2 a side elevation of the apparatus, and Figs. 3 and 4 are a plan and side elevation to a larger scale of the carriage upon which the lens is mounted. Figs. 5 and 6 are similar views to Figs. 3 and 4 of a carriage upon which the mirrors are mounted. Fig. 7 is a diagrammatic View showing a lens under test. p

Light from a suitable source is reflected toward the apparatus by means of amirror 10 and is condensed by a lens 11 on to the aperture of a diaphragm 12 through which it passes, after being rendered parallel by a lens 121, to a plane parallel glass plate 13. The surface of the glass plate is partially silvered so that part of the light is reflected and part transmitted by it. The transmitted portion of the light passes to a lens 14 which is under test and 15 is a mirror b which the light is reflected back through invention the lens is so mounted upon a cary and the carriage can be turned about an axis at right angles to the optical axis of the lens. -By adjustment of the lens the second nodal point of the lens can be positioned precisely in the axis about which the carriage turns. v

p The rotation of the carriage is effected by means of a rod which extends to the outer edge of the interferometer and is parallel to the axis of the lens, and a scale is provided so that the angle through which the lens is turned can be measured. Upon the.

rod and at right angles to it is mounted a bar whose distance from the axis of rotation of the lens can be adjusted, a scale being provided on the rod to enable the distance of the bar from the axis of rotation to the lens 14 to the plate 13 by which it is partly reflected toward the diaphragm l6 and forms an image of the aperture in the diaphragm 12. The other part of the beam passes to the mirror 17 from whence it is reflected back to the plate 13, part of the beam passing through the plate and combining with the beam that has passed through the lens 14.

The lens 14 is carried by a frame 141 free to move in a line at right angles to the optical axis of the lens upon a block 142 by means of a screw 140. The block 142 is mounted on a carriage 143 upon which it can be moved along the optical axis of the lens by means of a screw 144. .The mirror 15 is mounted on a frame 151 capable of movement upon a plate 152 the frame 151 being clamped to the plate 152 by screws 153, see igs. 5 and 6. The plate 152 is mounted on a carriage 154 and is capable of movement upon it and is held in position by a screw' 155. p

Th carriage 143 is turned-upon a pivot 191 by a rod 19 which extends to the outer edge of the apparatus over a scale 192 which indicates the number of degrees through which the rod is turned.

At right angles to the rod 19 is adjustably secured a bar 20 and the carriage154 is capable of sliding above the rod 19 and has attached. to it by a flexible connection 21, a weight (not shown), which weight always tends to maintain a lug 155 upon the carriage 154 in contact with the bar 20; The mirror is in this way moved away from the lens so that the center of curvature of" the mirror is always in the plane in which it is desired that the lens should focus its images; to maintain the mirror in this focal plane it must be moved a distance equal to the distance marked 23 as is shown in Fig.

'7. In full linesin'this figure 14 is the lens,

15 the mirror and 22 its focal plane in the case of an axial pencil; the dotted lines show the corresponding positions for an been polished with a View tdtheir partial oblique pencil.

The mirror 17 is mounted on a carriage 171 moving in grooves 172 and actuated by means of cords 173. 174 is a lens through which the recombined beams from the mirrors 15 and 17 pass.

On the plate 152 is also mounted a frame I 181 in which is another mirror 18, the frame 181 being clamped to the plate 152 by screws 18 The mirror 15 is convexand the mirror 18 concave, the mirror 15 eing removed when1 lenses of short focal length are being teste 9 When it is desired to test a lens it is placed rings upon the lens are observed and the parts of the lens requiring polishing are either marked on the lens or on a map of the same. When the parts ofthe lens have removal the lens is again mounted upon the carriage and the rod 19 is'turned so that the lens may be examined for oblique pencils, the interference rings are observed and the lens is partially treated to-remove the same and is then alternately treated for axial and oblique pencils until the desired accuracy is attained. I do not herein claim the apparatus shown and described in this application as claims therefor have been allowed in my Patent No. 1,347 ,133, granted July 20, 1920.

What I claim is 1. The process of testing and finishing.

lenses which consists inpassing axial beams of light through a lens under conditions such that interference rings are produced, correcting the faults indicated by the; interference rings and then passing oblique beams through the lens under conditions such-that interference rings are produced and correcting the faults indicated by these rings.

2. The process of testing and finishing lenses consisting in passing axial and oblique beams alternately through a lensunder conditions such that interference rings are produced and partially correcting the faults indicatedby these rings.

3. The process of testing and finishing lenses consisting in passing axial beams through a lens under conditions such that interference rings are produced, correcting the faults indicated by the interference rings, turning the lens about an axis at right angles to its optical axis and passing through its second principal point, passing oblique beams through the lens under conditions such that interference rings are produced and correcting the faults indicated by these rings.

4. The process of testing and finishing lenses, comprising testing a lens by alternately passing beams of light axially and obliquely therethrough, and making a partial correction after each test for the im- "perfections observed by said test.

beams of light, determining the effect of a lenscorrection on both axial and oblique beams, and then partially correcting said lens. to eliminate such imperfections.

6. The process of finishing and testing lenses, comprising passing axial beams through the'lens to be tested, reflecting said beams by a reflecting surface having its center of curvature in he plane in which it is desired to have thgjens focus its images, correcting the lens cording to this test, passing beams obliquely through the lens, adjusting the reflecting surface to maintain its center of curvature in the desired focal plane of the lens,- and correcting the lens according'to the second test.-

7. The process of finishing and testing lenses, comprising passing axial beams through'the lens to be tested to a reflecting surface, having its center of-curvature in the plane in which it is desired to have the lens focus its images, correcting the lens for defects observed by said test, turning the lens at an angle to said axial beams whereby it is subjected to beams passin obliquely therethrough, adjusting said re ecting surface to maintain its center of curvature in the desired focal plane of the lens and correcting the lens for defects observed by said second test.

8. The process of finishing and testing lenses, comprising passing axial beams.

through the lens to be tested to a reflecting surface in-the plane in which it is desired to have the lens focus its images, correcting the lens for defects observed by said test, turning the lens at an angle to said. axial beams, adjusting said reflecting surface in proportion to the angularity of the lens, and correcting the lens for defects observed by said second test.

9. The process of finishing and testing lenses, comprising passing axial beams through the lens to be tested to. a reflecting surface having its center of curvature in the 5 plane in which it is desired to have the lens focus its images, correcting the lens for defects observed by said test, turning the lens at an angle to said axial beams whereby it is subjected to "beams" passing obliquely therethrough, simultaneously adjusting said reflecting surface in proportion to the angularity ofthe lens'to maintain its center .of curvature in 'the desired focal plane of the lens, and correcting the lens for defects ascertained by means of the oblique beams.

London this 3rd da of J anuar 1919.

k F ANK T 7 MAN. 

